A building in the hot Midtown South marketplace at 315 Park Ave. South has been quietly put into contract to San Francisco-based Spear Street Capital for less than $250 million.

The sellers, Bijon Nassi and his son, Craig, of BCN Development, bought the 334,000 square-foot building right before the financial meltdown in 2007 for $265 million.

Last December, the $219 million in debt was sold by special servicer CWCapital through its former affiliate Rockwood Real Estate Advisors, along with Eastdil Secured’s Douglas Harmon and Adam Spies, to SL Green Realty Corp. for $218 million.

The Nassis then hired Harmon and Spies to market the entire kit and caboodle, which boasted $50 million in improvements, including two contemporary lobbies, new windows, 10 new elevators and a new roof.

Tenants include Credit Suisse, which has 275,000 square feet, of which 100,404 feet is up for sublease through CBRE; restaurateur Steve Hanson’s BR Guest; Boston Consulting; and office supplies chain Staples.

With all office leases expiring in April 2017, the 20-story building on the east side of the avenue between 23rd and 24th streets also has future residential potential.

The 16,000 square-foot floorplates have plenty of light, air and views as the surrounding buildings are much lower.

Spear Street is not a converter but has properties and relationships with technology and new-media tenants in markets such as Seattle, Austin, Boston and Washington.

Nearby, it owns the Crossroads Business Center in Bedminster, NJ, and Metro 101 in Iselin, NJ, but this will be its first building in the city.

The company did not return a call for comment.

Harmon and his Eastdil team recently sold the Sony building for $1.1 billion and were just hired by Time Warner to explore the sale of its Columbus Circle headquarters.

Neither the Nassis nor the brokers involved in the deal returned requests for comment.

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The Empire State Building is connecting LinkedIn with the full 22nd floor of 31,196 square feet, bringing its total space to 109,719 square feet.

The professional-networking site began its stay in the world landmark in a sublet on the 25th floor from Brennan Beer Gorman. In 2011, it became a direct tenant for the entire floor of 31,742 square feet.

In April of last year, the rapidly expanding company signed for another 10,396 square feet on the 24th floor. But even before construction started, it switched deals in September and expanded instead to the entire 23rd floor of 40,761 square feet.

To tide it over, LinkedIn has a one-year lease for 5,850 square feet on the 39th floor.

Sacha Zarba led the CBRE team representing LinkedIn.

Credit-focused building owner Anthony Malkin said, “They are growing and we have the room, but we don’t take a lot of these startups before they have IPOs.”

The deal also means the entire base of the tower up to the 25th floor is leased with Li & Fung USA, the FDIC, Coty, the World Monuments Fund and Shutterstock (which has the 20th and 21st floors, with an incredible terrace).

In the summer of 2006, there were 250 suites, with 40 percent of them vacant.

Asking rents in the higher floors are now around $55 a square foot. A block from floors 55 to 58 will soon be available.

The ESB was represented by a Newmark Knight Grubb Frank team led by William Cohen and Ryan Kass.

“The building has worked for them better than anyone could have imagined,” said Cohen, referring to LinkedIn. “Their cards don’t say ‘350 Fifth,’ they say ‘Empire State Building.’”

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Modell’s Sporting Goods is bulking up to 34,000 square feet at 1535 Third Ave. through a deal that adds 5,300 square feet of precious ground-floor selling space and 1,800 feet for lower-level storage to its current configuration.

The expansion will allow larger departments for ladies and children at the store on East 87th Street, which is opposite a forthcoming Whole Foods.

Modell’s was repped in-house by Doug Epstein, while building owner The Olnick Organization was represented by Matthew Krell and Amira Yunis of CBRE Retail.

The asking rent was $250 a square foot for the ground floor spaces.

Another 2,900 square feet of ground-floor retail, with 2,500 square feet of lower- level space, are still available.

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MoPub is moving from MePa to PaSo.

Mobile advertising company MoPub, which “serves” a billion ads a day, just signed a lease for a 13,121 square foot prebuilt on the 12th floor of 386 Park Ave. South.

It will relocate there in June from 71 Gansevoort St. in the Meatpacking District.

The building was purchased last year by a partnership led by the William Macklowe Co.

A new facade has been completed while upgrades of the streetscape, front entrance, lobby and elevator renovations continue.

Asking rents are in the $50 to $60 range, and nine full floors are available.

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Adding to the Midtown South mix, the interactive theater company Only Make Believe just signed a five-year deal for 2,500 square feet at 121 W. 27th St., where it will move from 1133 Broadway.

OMB performs for children in 55 hospitals and care facilities in the area.

Elliot Zelinger of Savitt Partners negotiated the five-year deal for the group, while Vijay Mehra of Professional Consortium represented the building ownership, which had an asking rent of $37 per square foot.

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The infertility practice Reproductive Medicine Associates of New York renewed its deal for 25,779 square feet at 635 Madison Ave in Midtown.

Daniel O. Horowitz and Jeffrey Peck of Studley represented RMA, while building owner, Ashkenazy Acquisition, which has asking rents of $90 to $100 per foot, was represented in-house by Andrew Wexler.